Every symbol in CommonLisp can refer to both a function and a value. Since
by itself refers to the value, we write
to refer to the function. The function special form is also used to create a LexicalClosure from a LambdaExpression. (A lambda expression may also be executed directly, but this actually macro-expands to the (function (lambda ... )) form.
In essence, all this means that function is a special form such that (funcall (function <whatever>) ...) evaluates to (<whatever> ...).
See SingleNamespaceLisp, FunctionLambda.